The present invention relates to automatic assembly systems and more particularly to systems for automatically fastening mating parts of an assembly having a dynamic joint.
Various attempts are shown in the prior art to deal with the problem of assembling a pair of mating parts having a pivot joint, such as a pair of scissors, with the desired tightness of the pivot joint.
U.S. Pat. No. 6,594,879 to Wheeler et al. is directed to setting the spacing between two or more moving, e.g., reciprocating, cutting elements of a power cutting tool. Wheeler teaches controlling the “clearance” between elements as they are fastened together.
U.S. Pat. No. 6,161,273 to Rivera et al. is directed to a method and apparatus for forming rivet joints that allow pivotal motion of the parts that are interconnected by such joints with a desired amount of clearance. Parts to be riveted together are aligned with each other and held in place on a parts support anvil, and a rivet is placed into aligned holes. A rivet support anvil is positioned against the head of the rivet to establish an initial condition. The rivet support is adjusted a required amount with respect to the parts support anvil prior to formation of the second head on the opposite end of the rivet. The rivet is allowed to move a controlled amount prior to formation of the second head, to provide the desired amount of clearance. The required amount of adjustment is determined empirically and is used thereafter in riveting a particular type of assembly, using fairly uniform parts and rivets of known composition. Once the correct amount of adjustment has been determined, the same adjustment relative to the initial condition will result in the desired clearance in each similar joint made thereafter.
U.S. Pat. No. 5,694,694 to Roskam is directed toward a pair of scissors having a screw holding the legs of the scissors together at the pivot joint to permit readjustment of the action by the user. A second screw provides for adjustment of the inclination of one blade relative to the other to adjust the tension and friction along the cutting edges.
U.S. Pat. No. 5,461,765 to Linden et al. is directed toward a method of manufacturing a pair of scissors wherein at least part of the pivot joint is molded of plastic material integrally with the plastic handle while the metal blades are held together. As a last step, the clearance at the joint is adjusted by applying a force sufficient to longitudinally displace the pivot joint to establish the desired amount of clearance, or by appropriately loosening the fastener prior to removing the assembly from the mold.